Re: Returning an empty sequence

*To*: mathgroup at smc.vnet.net*Subject*: [mg63293] Re: Returning an empty sequence*From*: dh <dh at metrohm.ch>*Date*: Fri, 23 Dec 2005 05:08:20 -0500 (EST)*References*: <dode3g$62d$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Hi Trevor, you must prevent "Sequence[]" to be evaluated before Switch is called. This can be done by "Unevaluated": f[n_] := Switch[n, 1, "foo", 2, Unevaluated[Sequence[]], 3, {"bar"}]; Daniel Trevor Baca wrote: > What's the right way to have an expression evaluate to an empty > sequence? > > I'd like ... > > f[n_] := > Switch[n, > 1, "foo", > 2, Sequence[ ], > 3, {"bar"}]; > > ... to work, but instead I get the message > > Switch::"argct": "Switch called with 6 arguments. Switch must be called > with an odd number of arguments." > > meaning that the Sequence[ ] is flattened in the rhs definition of f[ > ]. > > Is there a way to get f[ ] to evaluate to the empty Sequence[ ] (rather > than Null)? > > Trevor. >